Re: [LAU] OT - syncing partially out of sync video and audio in existing files - Linux-audio-user

11 Jun 2011

...
  Excerpts from pshirkey's message of 2011-06-10
21:56:06 +0200:
   Excerpts
from Ralf Mardorf's message of 2011-06-10 19:24:54 +0200:
> On Fri, 2011-06-10 at 18:57 +0200, Renato wrote:
> > On Fri, 10 Jun 2011 17:58:46 +0200
> > Philipp &lt;hollunder(a)lavabit.com&gt; wrote:
> >
> > > Hi,
> > > sorry for abusing this list for a mostly video editing question, 
but
 > I
> > > didn't find a proper list and knew that we have some video people
 on
 > > > this list.
> > >
> > > I'd like to fix some videos that have partially out of sync video
> and
> > > audio, meaning that beginning at a certain point in the video the
> > > audio is suddenly out of sync by a couple of seconds. There's no
> > > constant change, the delay seems fixed once it's there.
> > >
> > > I wonder how to fix such a thing. The files are xvid encoded  videos
 > > > and vbr mp3 audio inside avi
containers. I thought it should be
> > > reasonably easy to cut and move the audio (re-encode if 
unavoidable,
 > > > but I know it's in principle
possible without) and put it back in  a
 > > > container, but I didn't
manage.
> > >
> > > Can someone recommend a program/workflow that would allow this?
> > >
> > > I tried:
> > > - Avidemux: seems like actual editing is not what this program  was
 > > >   written for, couldn't figure
it out, but it seems close
> > >
> > > - openshot: couldn't figure out how to separate video/audio
> > >
> > > - kino: seems to only work with DV-files, apparently takes ages  to
 > > >   decode the file, doesn't seem
to be what I need
> > >
> > > - openmovieeditor: I figured it might work by dragging the file  to
 > > > both a video and an audio track,
but I got extremely garbled  audio
 > > > output, no idea what's wrong
> > >
> > > - cinelerra-cv: Doesn't start. No error message, it simply shows 
no
 > > >   window, nothing. Well, it does
something with the screen, but  it
 > > > shows nothing.
> > >
> > > - pitivi: Doesn't seem like it can play back the video. I can 
drag
 > the
> > >   video to the tracks and it starts to draw a waveform, I guess  no
 > > > video thumbnails because of:
gst.ElementNotFoundError: pngenc
> > >   Doesn't seem to be able to play the video.
> > >
> > > - kdenlive: would require me to install 30 additional packages,
> total
> > >   about 200MB, no thanks.
> > >
> > > I thought it would be a simple task, really nothing fancy. Seems
> like
> > > I was wrong.
> > >
> > > Regards,
> > > Philipp
> > >
> >
> > Hi, unfortunately can't give you a full solution, but only a hint: 
in
 > > mplayer with "-" and
"+" you can adjust audio/video syncronization  by
   >
multiples of 100ms (maybe you cand do finer, but I'm not sure).
 >
 > maybe you could then somehow record the output to a new file? 
 Thanks Renato, I've played with that already and know the approximate
 offsets, but that doesn't help much. I'm not sure screen recorders
 typically can pause and resume, and even then it would be less than
 optimal anyway due to the transcoding of both audio and video.

 Also, to clarify, those offsets are constant but only appear beginning
 at a certain point in the file, imaginary example: after 97 Minutes  the
  offset is suddenly approximately -9600ms. Hence
shifting the offset of
 the whole file doesn't help.

 I went through this a couple of years back with pretty much the same
 result. The general consensus round here was that it is not possible to
 shrink a video to fit with an audio track. Instead you should stretch
 the
 audio track to fit the video.

 I ended up using Blender to edit the video into chunks and align chunks
 of
 audio to fit as best as possible.

 I don't understand why it is not possible to resize a video track. It
 seems to me that dropping video frames is significantly easier
 programatically than time stretching audio. 
 I've only done this with one video so far, so I don't know whether it
 works fine in general, but in this case mencoder dropped a couple of
 seconds that were just black anyway, so no real loss. It was a fade out
 to black and I jugged down the time the moment it was black. I somewhat
 wonder how it was messed up, I suspect files were put together and some
 black frames were added without caring for audio, or something like
 that. Anyways, there's no loss of content with this file, which was with
 almost ten seconds delay by far the worst of the bunch. Ok, according to
 mplayer the file is now 13 seconds shorter instead of 9.55, but who
 cares as long as the result is fine.

 So it seems mencoder can just drop video frames. 
That's good to know. For references sake, what was the commandline that
you ended up using?

...
  I was also surprised about the speed. I guess it took
at most a minute
 per operation on this old cheap laptop and ~3h video, most likely it
 avoided re-encoding of anything, which is a good thing in my book. In
 contrast, just loading the video into kino would probably have taken an
 hour.

 Regards,
 Philipp